An investigation by the Australian Broadcasting Corporation (ABC) has alleged that the Adani Group's Australian operations have "previously unknown tax haven ties in the British Virgin Islands".

ABC's 'Four Corners' programme has uncovered the British Virgin Islands links of Gautam Adani's Australian ventures.

The Adani Group has promised a $22 billion windfall in taxes and mining royalty payments for Australia over the life of the Carmichael coal mine that received approval in Queensland. ABC quoted experts as saying that the "opaque web of companies and trusts" behind Adani's Australian assets gives it ample opportunity to minimise the tax it pays.

"Absolutely, Adani has put in place multiple ways in which they can minimise the amount of tax they pay in Australia and maximise profits if they choose in Caribbean tax havens," Adam Walters, research director at the consultancy Energy and Resource Insights, told Four Corners.

Adani Group's assets in Australia include the Abbot Point Coal Terminal near Mackay in Queensland, a terminal expansion project that is yet to get approval at Abbot Point, and a planned railway line of nearly 400 km from the port to the giant mine it wants to build in the Galilee Basin - aided by a subsidised loan of up to a $1 billion it is seeking from the Federal Government's Northern Australia Infrastructure Facility.

It was previously thought that Atulya Resources, a Cayman Islands domiciled company controlled by members of the Adani family, was the ultimate holding company for Abbot Point, the expansion project, and the railway.

However, filings in Singapore by privately-owned Adani companies show that a company registered in the British Virgin Islands, sits behind Atulya Resources, ABC reported.

It is variously described in the offshore company filings as ARFT Holding Limited, AFRT Holding Limited and Atulya Resources Family Trust.

The Adani Group's filings with Australia's corporate watchdog, ASIC, fail to mention this company, instead of continuing to list Atulya Resources as the owner.

The British Virgin Islands' company's apparent position at the apex of the structure is disclosed in the financial reports of a series of Adani companies controlled by Vinod Adani, also known as Vinod Shantilal Adani or Vinod Shah.

Vinod Adani, the older brother of Gautam Adani, has been under investigation in India over an alleged scam designed to shift money offshore, says ABC.

Investigating officers from India's Directorate of Revenue Intelligence accused Vinod Adani, along with ex-Adani Group employees and Adani companies, of executing a "planned conspiracy of syphoning off foreign exchange abroad and trade-based money laundering".

But the case was recently quashed by an adjudicator.

After hearing the Adani Group's defence, he ruled in late August that the transaction between Vinod Adani's companies and subsidiaries of Adani Enterprises was at "arms' length" and on legitimate commercial terms.

The Adani Group told authorities that Vinod Adani, as a non-resident Indian domiciled in Singapore, was an independent businessman with "no involvement" with the Adani group of companies.

However, Vinod Adani's intimate involvement in the ownership structure of Adani's Australian operations casts doubt on that claim.

Vinod Adani is the sole director of a number of Singapore-registered companies that control the Australian rail and port assets and are in turn owned first in the Cayman Islands and then in the British Virgin Islands, says ABC.

Another previously unknown British Virgin Islands-based entity provides a potential conduit for the Adani Group to shift potentially billions of dollars from its Australian operations offshore.

Carmichael Rail Australia Ltd BVI, registered in the British Virgin Islands, appears to directly control trusts established for the railway project in Australia.

One of those trusts is eligible to receive an "overarching payment" of $2 a tonne from the coal extracted from the Carmichael mine, rising by inflation for two decades. Carmichael is licensed to mine 60 million tonnes of coal a year.

Adam Walters says this gives Adani Group multiple ways to "skin it" and move revenue to the Caribbean: "Either to the Cayman Islands via Singapore or directly to the notorious tax haven of the British Virgin Islands."

Specialist tax lawyers and bankers who spoke to ABC's Four Corners say there is nothing unlawful about the structure Adani has established for its Australian operations.

Meanwhile, the Queensland government and business groups have defended the proposed Carmichael coal mine.

Queensland Premier Annastacia Palaszczuk has said the company will be held to account. "I've made it very, very clear to the people of this state that we have the strictest environmental conditions attached to this," Palaszczuk said.

Queensland Minister for Natural Resources and Mines Anthony Lynham has said the mine would be subject to "strict monitoring" throughout the construction process.